Variable resistor



oct 20, 1959 H. SCHWARTZ 2,909,751

-VARIABLE: REsIs'roR Filed July 23, 1956 2 Sheets-Sheet 2 i?. 7 F495. 5@y United States Patent() VARIABLE RESISTOR Harry Schwartz, Detroit,Mich., assignor to General Electric Company, a corporation of New YorkApplication July 23, 1956, Serial No. 599,419

6 Claims. (Cl. 3158-190) This invention relates to variable resistorsand more particularly to variable resistors of non-linear resistancematerial which provide a multiplicity of possible resistance values atany given voltage.

Non-linear resistors have found important applications in the electricalpower, communications and electronic industries. Heretofore, when aplurality of resistance values were necessary, a corresponding number ofindividual resistors were generally employed. The peculiarities ofdesign and operation of non-linear resistor devices has rendered itdifficult to develop a variable nonlinear resistor in the mannerordinarily used with linear resistors.

It is therefore an object of this invention to provide a variableresistor of non-linear resistance materials having a vast number ofpossible resistance values or levels. It is also an object of thisinvention to accomplish this result with a device which is relativelysimple in function and which is economical to manufacture.

Briefly stated, my invention comprises a body of nonlinear resistancematerial having a plurality of isolated conductive areas on both sidesand contact means for engaging at least two of the isolated conductiveareas of said resistance material.

My inventionfurther comprises a variable non-linear resistor having aplurality of isolated conductive areas on both sides, each of theconductive areas onL one side of said resistance material having a pathwhich, when projected through the resistance material, is coincidentwith at least a portion of the path of at least one -of the conductiveareas on the other side of said resistance material. n

My invention will be better understood by considering the followingdescription taken in connection with the accompanying drawings, in whichFigure 1 is a plan view of one embodiment of my invention showing anon-linear resistance material having longitudinally extending isolatedconductive strips thereon.

Figure 2 is a plan view of the reverse side of the resistance elementshown in Figure l.

Figure 3 is a perspective view, partly broken away, of the embodimentshown in Figures l and 2 in combination with contact means for engagingthe conductive strips.

Figures 4 and 5 are fragmentary plan views of a modiiication of theembodiment shown in Figures 1 and 2.

Figure 6 is a perspective View, partly in phantomoutline, of anotherembodiment of my invention.

Figures 7, 8, and9 are cross-sectional views of modiied forms ofresistance plates which can be used in th practice of this invention.

Referring to the `drawing and more particularly to Figures l, 2, and 3,a non-linear resistance material 10 is coated with a plurality ofisolated and longitudinally extending conductive strips 11 on one side.The other side is likewise coated with a plurality of strips 12. Theseisolated strips may be any conductive material such as brass, copper,stainless steel or aluminum. The conductive material may be applied tothe surface by depositing metal particles on the surface of theresistance material by spraying with metallic paint, by electrop'lating,by silk screen or llame plating or by like methods. The strips 12, inthe embodiment shown, are substantially perpendicularly disposed withrespect to the strips L11 on the opposite surface of the resistor.

Instead of strips of perpendicularly disposed conductive areas on bothsides of the resistance material, various configurations and variousnumbers of isolatedV conductive areas obviously may be employed in thepractice of this invention. For example, the paths may be disposed atangles with respect to each other which are greater or less than theninety degrees illustrated. Figures 4 and 5 illustrate a fragmentaryportion of a re'- sistance material in which the strips 13 and 14 onboth sides of resistance material 10 are at an oblique angle withrespect to the perimeters of the resistance material,

yrather than parallel or perpendicular as in Figures l and 2.

Each of the strips 11 and 12 in Figures 1 and 2 and strips 13 and 14 inFigures 4 and 5 are spaced from each other by a portion of theresistance material 10 and 10 respectively. lt has been found that thecurrent flowing across the resistor surface, transversely from oneconductive area to the adjacent conductive area on the same side of theresistance material, is negligible in relation to the currrent whichwill flow perpendicular to the surface through the resistance material.Accordingly, the conductive strips -11 and`1'2 (and 13 and 14) areeilectively isolated from each other.

One contacting assembly for use with the resistor shown in Figures l and2 is shown in Figure 3. In this gure the strips 11 and 12 are energizedthrough contacts 15 and cams 16 and `17. The contacts areinsulated'f'rorh each other and from the cams 16 and 17 by insulators 18and 19. Insulator 18 is contiguous to one surface of the resistancematerial, while insulator 19 is contiguous to the other surface.Embedded in insulators 18 and y1.9 are a series of contacts 15. Thesecontacts, which may be of any conductive material, are spaced so thateach contact is positioned in abutting relation with each one of theconductive strips `11 and 12. It will be noticed that each of thecontacts `15 are slightly longer than the width of the insulators 18 and19. The purpose of this is to ensure contact between the strips ofconductive material 11 and 12 and the cams 16 and 17. Cams 16 and 1 7are positioned -directly above and below the 4in sulators 18 and 19respectively. Cams 16 and 17 function to bring into circuit relation asmany or as few ofthe respective strips 11 and 12 as may be desired. Theentire assembly may be secured in the above described relationship by,for example, four screws 20, to the other end of which a nut (not shown)is attached. Knobs 21 and 22 are provided for rotation of cams 16 and 17respectively.

In operation, when `any one of the conductive areas on one side of theresistancematerial 10 is broughtinto circuit relation with any onev ofthe conductive areas .on they other side, current will pass through theresistor at Vthe point at which the projected paths of the resistancematerial coincide. Thus if the single strip 11 which is uppermost inFigure 1 and the single strip 12 which is at the far left in Figure 2are brought into circuit relation, the resistance path through thenon-linear resistor will be at the single point A. If, however, morethan one of the conductive areas on either or both sides are broughtinto circuit relation, the current will flow through a plurality ofpoints, either in parallel or in seriesparallel, depending on the numberand relation of the contacts, made. In effect, the single resistancematerial becomes a multitude of-isolated resistances at the points ofcoincidence of the projected paths of the conductive areas. It can thusbe seen that a vast number of possible resistance values may be achievedfor any given voltage by simply selecting the number and relation of theresistance areas which it is desired to bring into play.

In place of the contiguously placed electrical contact ployed. One suchmeans is by attaching leads to each of the conductive areas and formingelectrical contact with the leads at some position external to theresistor itself. Figure 6 illustrates one embodiment of this type ofcontacting means with a resistance plate in which the isolatedconductive areas on one side of the resistance plate are substantiallyaxially `aligned with the conductive areas on the other side. In thisembodiment, the conductive areas take the form of a plurality ofisolated spots '|23 on one side of resistance plate 25 and a pluralityof axially aligned isolated spots 24 on the opposite side. Leads 26 areattached to each of the isolated spots on one face of the resistanceplate 25 and leads 27 to the opposite side. These leads are attached attheir opposite end to contact 28 embedded in insulator 29. Cam 30contacts as many or as few of the contacts 28 as is desired. Knob 31 isused to control the action of cam 30. The leads 27 on the opposite sideof plate 25 lead to an identical insulator plate and cam assembly on theopposite side.

The operation of the embodiment shown in Figure 6 will be substantiallythe same as that of Figures 1, 2 and 3. Thatis, when a conductive spot23 is brought into circuit relation with a conductive spot 24 on theop-,

posite side, the resistance path through the resistance material will beat the single location between the aligned spots. By bringing aplurality of spots on both sides into the circuit a plurality ofisolated resistance paths vwill be set up in parallel. By bringing intocontact the proper conductive spots, the isolated resistance paths mayalso be connected in series relationship or in seriesparallel using theplates shown in Figure 6.

By a non-linear resistance material, I mean a material which willpresent a low resistance when subjected to a high voltage and a highresistance when subjected to ka comparatively low voltage. Such aresistance material is well knownin the prior art and one form thereofand method of making the same is shown and described in United StatesPatent 1,822,742, issued September 8, 1931,

of Figure 3, other suitable contacting means may be emto K. B. McEachronand assigned to the same assignee 'Y i' as the present invention. Apreferred form of nonlinear resistance material is that sold under thetrademark Thyrite by the assignee of the present invention. Thismaterial is made by pressing silicon carbide with a suitable ceramicbinder at high prmsure followed by N a firing operation at a hightemperature (approximately 1200 C.).

Additional variations in the resistance may be achieved by varying thedimensions of the conductive paths on one or Yboth sides of theresistance material. By varying the thickness of the resistancematerial, ythe resistance levels may be correspondingly varied. Some ofthe varied forms of resistance materials which may be used in thepractice of this invention are illustrated in Figures 7, l8 and 9,. Ifthese varying forms are combined with n suitable conductive areas, abroad range of resistance values may be obtained. 'I'he cross sectionsof Figures 7, 8 and 9 correspond to the substantially uniform crosssection of the resistance material 10 of Figures 1, 2 and 3.

In addition to making possible the use of a single nonlinear resistor inapplications where a plurality of individual resistors were heretoforenecessary, the resistors of this invention possess a large number ofpotential applications. They may be utilized for example in circuitshaving aging or drift characteristics which necessitate resistanceadjustments.

What I claim as new and desire vto secure by Letters Patent of theUnited States is:

1. A variable resistor comprising a plate of non-linear resistancematerial whose resistance varies inversely with the voltage, said platehaving a plurality of conductive areas on the opposite surfaces thereof,each of said conductive areas being isolated from the remainingconductive areas on the same surface, and cumulative contact means onthe opposite surfaces of said plate engaging in single circuit relationat least two of the isolated conductive areas on each surface so as topass current transversely through the plate.

2. A variable resistor comprising a plate of non-linear resistancematerial whose resistance varies inversely with the voltage, said platehaving a plurality of conductive areas on opposite surfaces thereof,each of said conductive areas being isolated from the remainingconductive areas on the same surface, each of the conductive areas onone surface of said resistance material having a path which, whenprojected through the resistance material, is coincident with at least aportion of the path 'of at least one of the conductive areas on theother surface of said resistance material, and cumulative contact meanson the opposite surfaces of said plate engaging in single circuitrelation at least two of the isolated conductive areas on each surfaceso as yto pass current transversely'through the plate.

3. A variable resistor comprising a plate of non-linear resistancematerial whose resistance varies inversely with the Voltage, said platehaving a plurality of areas on the opposite surfaces thereof having aconductive coating applied thereto, each of said conductive areas beingisolated from the remaining conductive areas on the same surface, andcumulative contact means on the opposite surfaces of said plate engagingin single circuit relation at least two of the isolated conductive areason each surface so as to pass current transversely through the plate. 4.A variable resistor comprising a plate of non-linear resistance materialwhose resistance varies inversely with -the voltage, said plate having aplurality of conductive strips on the opposite surfacesV thereof, eachof said strips being isolated from the remaining strips on the samesurface, the strips on one surface being angularly disposed with respectto the strips on the other surface, and cumulative Contact means onopposite surfaces of said plate engaging in single circuit relation atleast two of the isolated conductive areas on each surface so as to passCurrent transversely through the plate.

5. A variable resistor comprising a plate of non-linear resistancematerial whose resistance varies inversely with the voltage, said platehaving a plurality of conductive strips on the opposite surfacesthereof, each of said conductive strips being isolated from theremaining conductive strips on the same surface, the conductive stripson one side being substantially perpendicularly disposed with respect tothe strips on the other surface, and cumulative contact means onopposite surfaces of said resistance material engaging in singleicircuit relation at least two of the isolated conductive strips on eachsurface so as to pass current transversely through the plate.

6. A variable resistor comprising a plate of non-linear resistancematerial whose-resistance varies inversely with the voltage,`said platehaving a plurality of conductive areas on the opposite'V surfacesthereof, each of said conductive areas lbeing isolated from theremaining conductive area$ QI 1 the Same surface, said conductive areason 5 one surface being substantially axially aligned with the conductiveareas on the other surface, and cumulative contact means on oppositesurfaces of said plate engaging in single circuit relation at least twoof the isolated conductive areas on each surface so as to pass currenttransversely through the plate.

References Cited in the tile of this patent UNITED STATES PATENTS252,395 Odell Jan. 17, 1882 6 Jones Dec. 25, 1900 McEachron Sept. 8,1931 Siegel Feb. 27, 1934 Saville .Tune 25, 1940 Clancy Apr. 14, 1942Christensen Sept. 10, 1946 Schwartz July 24, 1956

